A transport network typically comprises a number of nodes, connected by links, for transporting information (whether representing data or voice) over a connection path. The latter is setup between a source node and a destination node of the transport network and may also comprise a number of intermediate nodes. Typically, in order to establish this connection path, a “connection setup” takes place.
Generally, for scalability and reliability reasons, network management functions such as path computation and connection setup are implemented in a distributed fashion. In other words, when a node gets a connection request (hence becoming the source node) from itself to any other node (the destination node) in the network, the source node first computes the path through the network independent of any other request in the system at that time. (Of course this requires that each node periodically get updates of the network status in terms of available capacity and resources). As such, connection setup between a source node and a destination node involves signaling to setup a cross-connect at every one of the intermediate nodes in the connection path. These cross-connects are setup between link resources assigned to the connection. In an optical transport network (OTN), the cross-connects are referred to as optical cross-connects (OXCs), the links are dense wavelength division multiplexed (DWDM) links, and the link resources are wavelengths assigned to individual connections. (It should be noted that the particular link resources are assigned via local nodal decisions rather than by the source node, which simply computes the connection path.)
Unfortunately, one of the problems inherent to a distributed implementation of network management functions is that of resource contention. For example, it is possible that cross-connect requests for two or more connection setups reach a common link in their path at the same time. If the requests are being setup from opposite directions, i.e., from alternate ends of the link, then the node on each side of the common link may allocate the same wavelengths to the different connection requests. This type of resource conflict may end up tying up wavelength ports and either causing unnecessary crankbacks or worse—deadlocks. The result may be extremely slow connection setup times and slow network restoration speed (in the event of a failure in the network)—not to mention a possible loss of revenue for service providers.